This invention relates to an alignment device and, more particularly, to an alignment device for use in a semiconductor circuit manufacturing apparatus having a resolving power capable of transferring a fine pattern having a minimum line width of an order of a submicron.
Among various types of exposure apparatuses usable as the semiconductor circuit manufacturing apparatuses, X-ray exposure apparatuses have become attractive because of their capability of transferring minute patterns having a minimum line width of the order of 0.5 micron or less and because throughputs as high as conventional optical exposure apparatuses are estimated.
Use of X-rays has been proposed also in the field of alignment between a mask and a wafer to be used in conventional optical exposure apparatuses or in the X-ray exposure apparatuses. However, the alignment through the X-rays is not yet practicable and, usually, reflection or diffraction of light is utilized. In the optical alignment, the light beam for alignment has a large diameter of approximately 10 microns and the surface of the wafer usually contains irregularities which cause scatter or irregular reflection of light. For these reasons, it is not so easy to stably obtain appropriate reflection light from alignment marks, which makes it difficult to achieve alignment of high accuracies of the order of 0.01 micron. This in turn leads to difficulities in accurately overlying patterns having minimum line width of the order of a submicron.